Pyrolysis refers to thermochemical decomposition of a solid feedstock, such as solid waste. Pyrolysis occurs at elevated temperatures without the participation of oxygen. This decomposition is accompanied by devolatization; that is, the escape of volatile gases from the solid feedstock. Hydropyrolysis is a type of pyrolysis that occurs in a hydrogen-rich atmosphere. Both pyrolysis in general and hydropyrolysis in particular are important processes in waste-to-energy (WTE) conversion. Furthermore, pyrolytic processes typically generate two output streams: a gas stream and a solid stream
Most WTE systems are through-systems, where waste is combined with fuel as required and then burned. For example, in a typical 50 megawatt (MW) incinerator plant, approximately 5,000 tons of waste may be burnt per day. Unfortunately, about 50% to about 60% of the waste processed is transformed into incompletely burned bottom ash, which has to be sent to a landfill. Additionally, fly ash is produced, which is classified as hazardous waste and must be processed as such. Burning raw municipal solid waste (MSW) also creates heavy metal emissions, especially from burning plastics, aluminum and batteries contained in a general unsorted waste stream. An expensive and complex off-gas treatment installation is necessary to reduce these emissions to levels required to meet environmental and other regulations. Also, if the MSW is wet, it generally costs more in energy to burn the waste than the actual amount of energy produced from the waste.
Moreover, typical pyrolytic processes only use indirect heating to create pyrolytic conditions, but having enough heat transfer from the pyrolytic device to the feedstock poses numerous operational issues. To overcome these limitations, longer travel paths for the feedstock have been implemented. Increased travel paths, however, increase the time of conversion and device size. As a result, process efficiency and device portability are diminished. The process takes longer and requires greater energy input. Thus, these pyrolytic processes have gas emissions which are unacceptable for current standards in many jurisdictions, are needlessly bulky and inefficient.